1. Field of the Invention
The present invention relates to brushless DC motors which function as drive motors for use in the industrial field of, for example, factory automation (FA) and office automation (OA), or as drive motors for electric automobiles. In particular, the present invention relates to a so-called gap winding motor, which is a smooth-armature winding motor in which armature winding for generating a rotating magnetic field is attached to an inner peripheral surface of an annular stator core which does not have salient magnetic poles (slots).
2. Description of the Related Art
Gap winding motors are known as motors with low torque ripples, and are commonly used. In general, a gap winding motor is structured as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2007-published on May 24, 2007. More specifically, the gap winding motor includes a cylindrical frame, a load-side bracket fixed to an end of the frame, a counter-load-side bracket fixed to the other end of the frame, a stator, and a rotor. The stator includes a stator core fixed to an inner peripheral surface of the frame and a plurality of thin-ring-shaped air-core coils for generating a rotating magnetic field (hereinafter simply referred to as air-core coils). The air-core coils are attached to an inner peripheral surface of the stator core. The rotor is disposed inside the air-core coils with air gaps therebetween in the radial direction.